1. Field of the Invention
The invention is directed generally to aiding frequency acquisition and, more particularly, to a method and device to extend the pull-in range of a timing recovery circuit for a storage device, such as an optical disc drive.
2. Related Art
Storage devices, such as disc drives and optical storage drives, use a spindle motor to rotate the storage disc. To ensure that information from the storage disc is obtained, it is necessary to know the rotational speed to correlate the data frequency of the storage disc.
One known method for obtaining the frequency includes moving a laser reading head to a hub of the storage disc and moving it back to a certain radius. Based on known radius and rotational speed, the data frequency can be estimated. However, this results in only an estimate of the frequency, and the error rate may be as high as 10% or even higher in some cases.
To account for this error, timing loop correction circuits have been employed to attempt to correct the error and pull-in the detected frequency so that the error is sufficiently small. However, known timing loop correction circuits may suffer from the problem with not being able to pull-in errors of relatively larger corrections. By way of example, a timing loop correction circuit may only be able to pull-in a frequency error of about 0.5%. If the frequency error is greater, the storage device may be unable to lock in the frequency and access the data. Accordingly, it would be desirable to provide improved frequency error pull-in for storage devices and, in particular, for optical storage drives.